Device for stabilizing a web

Abstract

The invention relates to a device ( 11 ) for stabilising the transport of a material web ( 12 ) on the upper face of an air-permeable machine clothing ( 10 ), in particular a fibrous web. The device is located on the underside of the machine clothing directly upstream of an intake nip in the direction of travel ( 17 ) of the web, said nip being formed by a roll ( 5 ) and the machine clothing, and comprises a first negative-pressure zone ( 19 ) and at least one vacuum opening ( 20 ) that faces essentially in the opposite direction to the direction of travel of the web, communicating with the first negative-pressure zone of the device. This permits the boundary layer ( 23 ) of air that is carried along by the underside of the machine clothing to be at least partially sucked from said clothing into the first negative-pressure zone.

1. An apparatus for stabilizing the transport of a material web guided on a transport surface of an air-permeable covering comprising:
 a first negative-pressure zone; and 
 at least one suction opening arranged to face essentially in a direction opposite a web running direction and to communicate with the first negative-pressure zone in such a manner that a boundary layer of air carried along by a bottom side of the air-permeable covering is at least partially suctioned into the first negative-pressure zone, 
 wherein the first negative-pressure zone is positioned on a side of the air-permeable covering opposite the material web. 
 
     
     
       2. The apparatus according to  claim 1 , wherein several suction openings are arranged one after the other in relation to a transverse direction of the air-permeable covering. 
     
     
       3. The apparatus according to  claim 1 , wherein the at least one suction opening extends in a transverse direction in relation to the air-permeable covering. 
     
     
       4. The apparatus according to  claim 3 , wherein the suction opening extends essentially over a width of the air-permeable covering. 
     
     
       5. The apparatus according to  claim 1 , further comprising one guide element which is arranged such that a boundary layer of air carried along by the bottom side of the covering is diverted at least in part from the air-permeable covering and to the suction opening. 
     
     
       6. The apparatus according to  claim 1 , further comprising a guide element arranged in front of the first negative-pressure zone looking in the web running direction. 
     
     
       7. The apparatus according to  claim 6 , wherein the guide element has a guide face. 
     
     
       8. The apparatus according to  claim 7 , wherein the guide face faces with its one end side in the opposite direction to the web running direction toward the bottom side of the air-permeable covering, and with an other end side in the direction of the suction opening which faces in the opposite direction to the web running direction. 
     
     
       9. The apparatus according to  claim 8 , wherein the end of the guide face facing in the direction of the bottom side of the air-permeable covering is arranged in the direct vicinity of the bottom side of the air-permeable covering. 
     
     
       10. The apparatus according to  claim 6 , wherein the guide element is constructed such that, in a region of an end facing the bottom side of the air-permeable covering, a cross section tapers to a point in the direction of the air-permeable covering. 
     
     
       11. The apparatus according to  claim 6 , wherein the guide element extends essentially over an air-permeable width of the air-permeable covering. 
     
     
       12. The apparatus according to  claim 1 , wherein at least one suction opening faces essentially in the direction of the bottom side of the air-permeable covering, and communicates with the first negative-pressure zone of the apparatus. 
     
     
       13. The apparatus according to  claim 12 , wherein several suction openings are arranged one after the other in the transverse direction of the air-permeable covering. 
     
     
       14. The apparatus according to  claim 12 , wherein at least one suction opening extends in a transverse direction in relation to the air-permeable covering. 
     
     
       15. The apparatus according to  claim 14 , wherein the suction opening extends essentially over a width of the air-permeable covering. 
     
     
       16. The apparatus according to  claim 1 , wherein the first negative-pressure zone is directly in front of an intake nip formed by a roller and the air-permeable covering. 
     
     
       17. The apparatus according to  claim 16 , wherein a second negative-pressure zone is formed between the first negative-pressure zone and the intake nip. 
     
     
       18. The apparatus according to  claim 17 , wherein the first and the second negative-pressure zones coincide. 
     
     
       19. The apparatus according to  claim 17 , wherein at least one of the first or second negative-pressure zone is formed in the region between the intake nip, a doctor blade and the guide element. 
     
     
       20. The apparatus according to  claim 17 , wherein a third negative-pressure zone acting on the bottom side of the covering is formed in front of the guide element looking in the web running direction. 
     
     
       21. The apparatus according to  claim 16 , wherein a doctor blade acting on the roller is arranged directly in front of the intake nip such that a boundary layer of air carried along by the roller is diverted from the roller. 
     
     
       22. The apparatus according to  claim 1 , wherein the apparatus is arranged in a transfer apparatus. 
     
     
       23. The apparatus according to  claim 22 , wherein the transfer apparatus is arranged between a drying apparatus and a winding apparatus of a tissue machine. 
     
     
       24. The apparatus according to  claim 23 , wherein the drying apparatus is a Yankee drying cylinder. 
     
     
       25. The apparatus according to  claim 1 , wherein the covering is at least one of structured, has a rough surface, or is voluminous. 
     
     
       26. The apparatus according to  claim 1 , wherein the covering is a belt, embossing belt, felt, embossing felt, or membrane. 
     
     
       27. The apparatus according to  claim 26 , wherein the covering is a Spectra membrane or TAD (through air dryer) belt. 
     
     
       28. The apparatus according to  claim 1 , wherein the material web comprises a fibrous web. 
     
     
       29. A method for stabilizing the transport of a material web guided on a transport surface of an air-permeable covering comprising:
 creating a first negative-pressure zone, and 
 at least partially suctioning a boundary layer of air carried along by the bottom side of the air-permeable covering into the first negative-pressure zone through at least one opening arranged to face essentially in a direction opposite a web running direction, 
 wherein the first negative-pressure zone is created on a side of the air-permeable covering opposite the material web.